1. Field of the Invention
The present invention relates to a method, system, and computer program product for determining a metric to use to determine whether to generate a low space alert.
2. Description of the Related Art
In Storage Area Networks (“SAN”), storage space is hosted on dedicated storage systems and accessed by the consuming applications across a fibre channel network. Storage space in a storage system is divided into storage pools and is provisioned from the pools in the form of volumes which are assigned to the host server(s) running applications. The hosts view the volumes as disks or logical units. In typical deployments, the storage space allocated to a volume is not entirely used by the host applications, but more storage space is used over time. Thin provisioning is a virtualization technology that assigns a large virtual space to a volume that a host views as if the full space is allocated. However not all the space is actually allocated to the volume until needed by the host. Thus, thin provisioning has the appearance of having more physical storage space than actually available, where space is allocated just as needed. With thin provisioning, the virtual storage space of a volume on the storage system is not fully realized at volume-creation time. The necessary physical space is dedicated to the virtual volume only as the applications starts using the space in the volume. Thin provisioning minimizes allocating unused space to volumes in the storage environment because real physical space is allocated to the volume only when actually needed.
Normally, provisioning more storage space than physically available (over provisioning or over allocating) is not problematic because typically not all of the assigned virtual space is used. However as space demands increase, then the storage system may run out of physical space for unallocated virtual space. If this occurs, applications may not receive access to the space they need and may not be able to complete processes, resulting in errors. It is therefore important to effectively monitor thin provisioned space usage in pools and storage systems. Current techniques for such monitoring consider either virtual or physical space.
Monitoring virtual space entails computing the ratio of total assigned virtual storage space to total physical storage system space. For example if the space assigned in all the volumes is 15 TB, but the storage system only has 10 TB of space, this results in a virtual allocation percentage of 150% (or an over-provisioning percentage of 50%). This metric indicates how much space has been promised to applications compared to the space that is actually available in the pool or storage system.
Another technique is to monitor physical space which involves computing the ratio of used volume space to the total pool or storage system space. For example if all the volume space used by virtual storage is 8 TB, and the pool or storage system has 10 TB of total physical space, then there is a usage percentage of 80%, i.e. the pool or storage system is 80% used, or only 20% available. This metric provides an indication of whether the storage system is running out of space, and how quickly it is running out of space. These different metrics may be used to monitor thin provisioned space usage in a storage pool or system.